In the oil and gas industry, production or exploration wells are provided with one or more well bore control devices, such as a blow out preventer or riser control device for sealing the well bore in the event of an emergency in order to protect personnel and the environment.
Most well bore control devices are known as blow out preventers (BOPS) and include various sets of rams. There are three basic types; pipe rams for closing around a pipe or tubular passing through the well bore control device, blind rams for sealing the well bore in the absence of a tubular passing through the device and shear rams for cutting through any tubular present in the well bore. All sets of rams are mounted perpendicular to the well bore, which is vertically orientated. In the event of a blow out from an over pressure situation in the well, the shear rams can be activated to sever a tubular disposed in the well bore and passing through the well bore control device and so seal the well bore and prevent escape of well fluids. Shear rams are actuated to move in a horizontal plane and are driven by in line pistons. Most existing BOPs and well bore control devices have a number of drawbacks, for example, sealing is generally achieved using elastomeric seals and these seals can be limited with more aggressive wells with high temperature and high pressure fluid requiring containment. In addition, the existing structure of inline pistons creates a very large and heavy structure which can be difficult to manoeuvre and expensive to manufacture.
Improved sealing of a well bore can be achieved by using valves to seal the throughbore, but most available valves, such as ball valves with a hardened cutting edge, can only cut through a very limited range of tubulars or conduits and generally most of these are a relatively small diameter 2 to 3 inches, such as coil tubing.
UK patent GB2454850B discloses an improved well bore control valve which is more compact than traditional BOPs in which cutting gates and actuators are arranged in parallel to reduce the overall length of the device. Operation of the actuators pulls cutting blades and gates across the throughbore in opposite directions to provide a shear force to cut tubulars in the well bore and subsequently the gates seal the well and engage two separate seals to provide independent metal to metal seals.
It is desirable to provide further modifications to the aforementioned well bore control device to provide further enhancements in sealing, seal maintenance and replacement and general device maintenance.